Yasuhiro Akai

Hypoxia has been proposed as an important microenvironmental factor in the development of tissue fibrosis; however, the underlying mechanisms are not well defined. To examine the role of hypoxia-inducible factor-1 (HIF-1), a key mediator of cellular adaptation to hypoxia, in the development of fibrosis in mice, we inactivated Hif-1alpha in primary renal epithelial cells and in proximal tubules of kidneys subjected to unilateral ureteral obstruction (UUO) using Cre-loxP-mediated gene targeting. We found that Hif-1alpha enhanced epithelial-to-mesenchymal transition (EMT) in vitro and induced epithelial cell migration through upregulation of lysyl oxidase genes. Genetic ablation of epithelial Hif-1alpha inhibited the development of tubulointerstitial fibrosis in UUO kidneys, which was associated with decreased interstitial collagen deposition, decreased inflammatory cell infiltration, and a reduction in the number of fibroblast-specific protein-1-expressing (FSP-1-expressing) interstitial cells. Furthermore, we demonstrate that increased renal HIF-1alpha expression is associated with tubulointerstitial injury in patients with chronic kidney disease. Thus, we provide clinical and genetic evidence that activation of HIF-1 signaling in renal epithelial cells is associated with the development of chronic renal disease and may promote fibrogenesis by increasing expression of extracellular matrix-modifying factors and lysyl oxidase genes and by facilitating EMT.

CTGF plays a significant role in the development of renal fibrosis by mediating the fibrotic effects of transforming growth factor (TGF)-beta(1) and has been shown to be hypoxia inducible in human breast cancer cells. It has been suggested that hypoxia is an important underlying cause for the development of renal fibrosis through the modulation of profibrotic genes. One of the key mediators of the cell's response to lowered oxygen environments is hypoxia-inducible-factor-1 (HIF-1), a basic helix-loop-helix transcription factor, which enables cells to adapt to hypoxia by regulating the expression of genes involved in increasing oxygen availability (VEGF, erythropoietin) and enhancing glucose uptake and metabolism (Glut-1, PGK). In this paper, we have used primary tubular epithelial cell cultures from a tetracycline-inducible-Hif-1alpha knockout murine model to further elucidate the role of Hif-1 in the hypoxic-induction of Ctgf expression. We show that hypoxia response elements present upstream of Ctgf enable direct interaction of Hif-1 transcription factor with the Ctgf promoter, resulting in increased transcription of Ctgf mRNA. Cells deficient in Hif-1alpha were incapable of inducing Ctgf mRNA in response to hypoxia, suggesting an absolute requirement of Hif-1. Furthermore, the observed Hif-1-mediated hypoxic stimulation of Ctgf expression was found to occur independently of TGF-beta(1) signaling. Our findings have important implications for a number of fibrotic disorders in which hypoxia, CTGF, and TGF-beta(1) are involved, including renal, dermal, hepatic, and pulmonary fibrosis.

Chronic hypoxia accelerates renal fibrosis. The chief mediator of the hypoxic response is hypoxia-inducible factor 1 (HIF-1) and its oxygen-sensitive component HIF-1alpha. HIF-1 regulates a wide variety of genes, some of which are closely associated with tissue fibrosis. To determine the specific role of HIF-1 in renal fibrosis, we generated a knockout mouse in which tubular epithelial expression of von Hippel-Lindau tumor suppressor (VHL), which acts as a ubiquitin ligase to promote proteolysis of HIF-1alpha, was targeted. We investigated the effect of VHL deletion (i.e., stable expression of HIF-1alpha) histologically and used the anti-HIF-1alpha agent [3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole] (YC-1) to test whether inhibition of HIF-1alpha could represent a novel approach to treating renal fibrosis. The area of renal fibrosis was significantly increased in a 5/6 renal ablation model of VHL-/- mice and in all VHL-/- mice at least 60 wk of age. Injection of YC-1 inhibited the progression of renal fibrosis in unilateral ureteral obstruction model mice. In conclusion, HIF-1alpha appears to be a critical contributor to the progression of renal fibrosis and could be a useful target for its treatment.

OBJECTIVE: To investigate plasma concentrations of adrenomedullin in patients with septic shock and the potential association of these concentrations with relaxation of vascular tone. DESIGN: Prospective, case series. SETTING: Department of Emergency and Critical Care Medicine, Nara Medical University. PATIENTS: Twelve patients who fulfilled the clinical criteria for severe sepsis or septic shock (as defined by the Members of the American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference Committee) and 13 healthy volunteers. INTERVENTIONS: Arterial blood samples were obtained via a 20-gauge cannula inserted into each patient's radial artery. MEASUREMENTS AND MAIN RESULTS: After extraction and purification, plasma adrenomedullin was measured by radioimmunoassay. Systemic vascular resistance index, pulmonary vascular resistance, cardiac index, and stroke volume index were determined with a thermodilution catheter. The mean plasma concentration of adrenomedullin was markedly higher in patients than in controls (226.1 +/- 66.4 [SEM] vs. 5.05 +/- 0.21 fmol/mL, p < .01). Moreover, these concentrations correlated significantly with cardiac index, stroke volume index, and heart rate values, and correlated significantly with decreases in diastolic blood pressure, systemic vascular resistance index, and pulmonary vascular resistance index values. CONCLUSIONS: Enhanced production of adrenomedullin in patients with septic shock may contribute to reduced vascular tone, hypotension, or both. More data are needed to clarify the role of adrenomedullin in the regulation of vascular tone in this patient population.